The Doctor and Romana learn the second segment of the Key to Time is on the planet Calufrax. Yet they arrive on a planet called Zanak, which has been hollowed out and fitted with hyperspace engines, allowing its insane, half-robot Captain to materialise it around smaller planets and plunder their resources.

• BBC
• Tom Baker
• Mary Tamm
• John Leeson
• Bruce Purchase
• Andrew Robertson
• Rosalind Lloyd
• David Warwick
• David Sibley